Building threat simulator for multi-port radar and warfare systems

Generally, precise testing for many types of multiple-input devices requires accurate control over the amplitude and phase of all stimulus signals applied to the inputs of the unit under test (UUT). Examples include phased-array radar systems and multiple-input/multiple-output (MIMO) devices used in commercial communications and wireless networking. In these applications, precise control makes it possible to accurately simulate parameters such as the angles of arrival of incident signals.

This type of testing is useful in research, product development, design verification, manufacturing, and calibration. In all cases, a test solution that provides flexible synchronisation of test signals can help reduce test time—an advantage that is especially beneficial in the manufacturing process. As an example, let's consider the process of developing a test platform to evaluate the performance of a four-port UUT. The results provide significant benefits from technical and operational perspectives.

The problemThe testing of multiple-input receivers often presents a key challenge: delivering the desired signal at the end of long test cables. Creating an accurate signal simulation has two major requirements. One is the need to measure changes in phase and amplitude at the UUT, not in the test equipment itself. The other is the need to make real-time corrections to the amplitude and phase of each waveform. This level of control ensures proper alignment of the simulated incident signal in the presence of reflected signals from the inputs of the UUT.

For the four-port radar receiver, the challenge was to create a system that could serve as both a threat simulator and a receiver calibrator. To thoroughly test the UUT, the system had to provide phase accuracy of less than 1 degree from 100MHz to 20GHz—and do so at the end of 6-ft test cables. To support the intended usage model, the system had to meet two additional criteria: maintain its calibrated accuracy for at least 12 hours, and eliminate the need to manually attach and detach calibration standards during a test (i.e., support hands-free calibration).

Figure 1: The simulator/calibrator system has two major sections: the coherent, wideband stimulus side and the RF correction side.

Sketching the solutionThe system has two major sections: coherent wideband stimulus and RF correction (figure 1). The stimulus section generates two sets of complex waveforms that simulate real-world signals. The other section performs 12-term error-corrected stimulus measurements at the UUT and provides feedback for correction of the RF and microwave signals.

Although it isn't shown, the system also includes a host PC running a test executive. The PC is linked to the LXI-compliant instruments through LAN connections and a router.

The left-hand side of figure 1 includes two types of instruments: vector signal generators and arbitrary waveform generators (AWGs). For the vector signal generator, the key specifications are phase accuracy of less than 1 degree and an amplitude imbalance of less than 0.1 dB. Key attributes of the AWG are fast waveform switching and waveform resolution of less than 0.25 ns.